The skeletal system is categorised into three main parts, each with its distinct functions:
The Axial Skeleton
This segment spans from the skull to the tip of the tail and includes vital structures such as the skull, mandible, vertebrae, and sternum. It forms the central axis of the body, providing support and protection to vital organs like the brain, spinal cord, and heart. These items are highlighted in blue on the diagram.
The Appendicular Skeleton
Comprising the pectoral (front) and pelvic (hind) limbs, along with the shoulder and pelvic girdles, which attach them to the axial skeleton. The appendicular skeleton facilitates the movement and locomotion of the animal, allowing for agile and coordinated motion. These items are highlighted in pink on the diagram.
The Splanchnic Skeleton
Found in dogs and cats, it consists of the os penis, a small bone within the penis tissue. Although less pronounced in its overall function, the splanchnic skeleton plays a specialised role in reproductive physiology.
The Skeletal System fulfills various crucial functions:
Protection
Acting as a robust framework, the skeletal system shields delicate organs, such as the brain and vital viscera, from potential injuries or trauma.
Locomotion
The arrangement of bones, joints, and muscles enables animals to engage in dynamic movements, supporting their ability to walk, run, jump, and engage in other physical activities.
Attachment of Skeletal Muscles
Bones provide anchor points for skeletal muscles, enabling movements of the body and limbs. This allows dogs to perform everyday activities like jumping, fetching, and chewing.
Production and Storage of Blood Cells
Within certain bones, the bone marrow functions as a site for the production of red and white blood cells and platelets. These blood cells play a vital role in immune function and oxygen transport.
Storage of Minerals
Bones serve as repositories for essential minerals such as calcium and phosphorus. When the body requires these minerals for various physiological functions, bones release them into the bloodstream.
By comprehending the different parts of the skeletal system and their essential functions, we gain a deeper understanding of how this remarkable framework supports and sustains the body of our canine companions.
From a hydrotherapy perspective, the vertebrae, ribs, and sternum are of paramount importance among the bones in the axial skeleton.
Vertebrae
The vertebral column constitutes a series of numerous bones aligning along the body’s midline, extending from the base of the skull to the tip of the tail. These bones are categorised into different regions based on their locations, each serving distinct purposes:
Cervical (C) region: Pertaining to the neck area.
Thoracic (T) region: Encompassing the chest or thoracic region.
Lumbar (L) region: Located in the lower back or abdominal region.
Sacral (S) region: Situated in the pelvic area.
Caudal (Cd) region: Corresponding to the coccygeal or tail section.
These identifying letters are commonly found on clinical history reports received from referring veterinary surgeries, hence it is essential for hydrotherapists to be familiar with them. The number of vertebrae in each region is species-specific and presented as a formula. For both cats and dogs, the number of vertebrae is the same, with variations as follows:
C7:T13:L7:S3:Cd20-23
The count of coccygeal vertebrae may differ depending on the animal’s tail length, and some breeds or docked individuals may have fewer coccygeal vertebrae.
The vertebral column serves several crucial functions:
- Providing rigidity to the body axis and aiding in maintaining posture.
- Enclosing and safeguarding the delicate spinal cord.
- Protecting and shielding underlying structures.
In all mammals, there are seven cervical vertebrae, with the first two possessing individual names that signify their significance in neck movement. The first vertebra is known as the atlas, while the second is referred to as the axis. Together, they form a specialised pivot joint that facilitates head rotation and movement.
In adult cats and dogs, the sacral vertebrae fuse to form the sacrum, which creates a fibrosynovial joint with the ilium’s wing, constituting the sacroiliac joint.
The vertebrae are classified as irregular bones, representing a crucial part of the vertebral column’s structure, function, and overall significance in the body’s mechanical support and protection.
Ribs and Sternum
The ribs and sternum together create the framework of the bony thoracic cage, providing a protective enclosure for the chest organs.
Each rib consists of two parts: a bony portion that articulates with the thoracic vertebrae and a cartilaginous portion that articulates with the sternum.
In both dogs and cats, there are a total of thirteen pairs of ribs. The first eight ribs directly attach to the sternum, making them sternal ribs. Ribs 9 to 12 are known as false ribs or asternal ribs because they connect to the next rib rather than directly to the sternum, forming the costal arch. The thirteenth rib is referred to as a floating rib since its cartilage end does not attach to the sternum or another rib.
All the ribs are classified as flat bones, contributing to the robust structure of the thoracic cage and playing a critical role in safeguarding vital organs within the chest.
Appendicular Skeleton
The appendicular skeleton encompasses both the forelimbs and hindlimbs, along with the shoulder and pelvic girdles, which attach these limbs to the body. Unlike the forelimb, the hindlimb does have bony attachments to the thorax, providing additional stability during movement. When a quadruped runs, the forelimb’s muscles play a crucial role in absorbing the impact of the body’s weight.
In some primates that walk on their hindlimbs, a clavicle (collar bone) serves as part of the attachment of the forelimb to the upper body. However, this clavicle is often absent or vestigial (no longer serving a function) in many quadrupeds. Some dogs may have a vestigial clavicle embedded in muscle near the shoulder joint, while others lack it entirely. On the other hand, cats do possess a clavicle, though it does not form a joint with any other bones.
The Forelimb
The forelimb comprises several bones, including the scapula, humerus, radius, ulna, carpal, metacarpal bones, and the phalanges of the digits.
The Hindlimb
The hindlimb is made up of the femur, tibia, fibula, patella (knee cap), tarsal, metatarsal bones, and the phalanges of the digits.
The hindlimbs are connected to the body through the pelvis, which consists of two hip bones. Each hip bone is composed of three bones: the ischium, ilium, and pubis. These three bones converge at the acetabulum, forming the socket in which the head of the femur sits to create the hip joint.
Additionally, the patella, also known as the knee cap, is a sesamoid bone, meaning it is embedded within a ligament rather than forming part of a joint. This structure provides stability and support during locomotion.
Splanchinic Skeleton
The splanchnic skeleton comprises bones that form within soft tissues and remain unattached to other parts of the skeletal system.
In dogs and cats, the penis is the sole bone in this category, exclusively found in males of the species.
Cattle possess a unique bone known as the os cordis, located within the heart.
Birds have specialised bones surrounding their eyeballs, providing reinforcement and strength to accommodate their large eyeballs.